50mm disc adaptor is mounted to the back of chuck which mounts to any lathe using a 4 jaw chuck quickly and easily. The chuck is made from 1/4" phenolic plates that give you years of service and performance.Unique Self Centering Mechanism. The Longworth Style Chuck grips your project by simply rotating the phenolic plates. This moves the gripper buttons in or out to the exact position you need. The chuck can grip your project from the outside (outside compression mode) or the inside (inside expansion mode). Once the gripper buttons are firmly up against your project, secure them by tightening the wing nuts.